A currently influential hypothesis is that changes in cognitive function with advancing age are the result of a generalized slowing of nervous system function. There are findings that are inconsistent with that hypothesis. They are, however, consistent with the interpretation that age particularly affects response-related processes. The research proposed in this application explores that possibility. The feasibility of two approaches will be examined. one approach will test the hypothesis that processing that does not lead to an overt response is either unaffected by aging or less affected than processing leading to a response. The second approach will test the hypothesis that the degradation of performance that occurs when two tasks must be done simultaneously is largely due to competition for a limited-capacity response selection stage and that the effects of this bottleneck are more severe for older than for younger adults. If these hypotheses are supported by the results, the research would indicate the need for refinement of theoretical explanations of age-related changes in cognitive function and could provide direction in the search for the biological substrates for the affects of age on behavior.